Rock-drill.



V. J. OBRIEN.

ROCK DRILL.

APPLICATION HLED APR.8. I9I3- RENEWED FEB. 3.1914.

Patented NOV. 30, 1915.

5 SHEETS-SHEET I.

` A ROCK DRILL. -APPLCATION FILED APR.8. i913. RENEWED FEB. 3. l914.1,162,249.

Pateted Nov. 30, 1915,

5 SHEETS-SHEET Z.

A v.1. Q'BRIEN.

ROCK DRILL. PPLICATION FILED APR-8 l9l3 RENEWED FEB. 3,194,

Patented Nov. 30, 191.5,

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ROCK DRILL. APPLlc/mow man Ame. 1913. RENEwED fz-:8.3.19l4.

Patented Nov. 3,0, 1915.

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VINCENT JOHN OBRIEN, OF DENVER, COLORDO.

ROCK-DRILL.

Specification of Letters Patent.

Patented Nov. 3G, 19rd.

Application filed April 8, 1913, Serial No. 759,593. Renewed February 3,1914. Serial No. 816,316.

To all 'whom it lmay concern p Be it known that I, ViNoENT JOHN OBRIEN,citizen of the United States, residing at 514e Galapago street, in thecity and county of Denver and State of Colorado, have invented certainnew and useful Improvements infRock-Drills; and I do declare thefollowing to be a full, clear, and exact descriptionfof the invention,such as will enable others skilled in the art to which it appe'tains. tomake and use the same,.ref

Ierence being had to the accompanying draw-- in the art, so far as Iunderstand it, consists 1n making prov1sion tor a graduated exhaust fromthe hammer cylinder, the exhaust being regulated to harmonize with thesupply of air to the cylinder for reciprocating .the hammer. In otherwords, the throttle valve is so constructed that .as the. supply of; airto the hammer cylinder for reciprocating the latter is increased, theexhaust port in the valve is correspondingly increased. This feature hasan important advantage over constructions heretofore in vogue and inwhich a permanent or' fixed exhaust is employed. In constructions of thelast-named character it is necessary that the exhaust shall be sorestricted as to hold the cylinder valve in the closed position duringthe re- 'seriously interferes with the lective opera--l tion of theconstruction.v M improved con-` struction, whereby the exhaust isregulated in harmony with the supply of air *to the drill cylinderkovercomes-this difficulty and makes itk practicable vto obtain not onlya lconstruction whereby the pressure withr vtheifeed cylinder 1s lessduring the return hard blow with the travel of the hammer no rmal butalso makes it practicable to obtain a relatively rapid light blow. Thisis accomplished by opening the exhaust port of @0 the throttle valve topermit the maximum volume of motive iiuid to pass therethrough, while atthe same time the maximum amount of motive fini-d is entering the drillcylinder'. In this case the result is that by increasing the exhaust,the pressure on the rear and enlarged extremity ot the cylinder valveupon which reliance is made for retaining he latter in the closedposition during the return stroke of the hammer, is so reduced' that thevalve will open under the action of the contant live air pressure on ayshoulder of the valve, after the hammer has traveled only a smallproportion ot' the length of the drill cylinder between the rearextremity of 7s the hammerand the rear end of said cylinder. Thisopening movement ot the valve d permits the entrance of the live air fordriv.h ing the hammer forwardly and in this manner a very rapid, lightblow may be obso tained, which is impossible in constructions havingafixed or non-varying exhaust pas sage. f A

Another feature of novelty consists in a stroke of the hammer thanduring the forward 'stroke thereof. 1This result is obtained by takingthe air from the feed cylinder which produces the returnmovement oit thehammer and so arranging the ports and passages thatthe amount ot airtaken from the feed cylinder is greater than that which is deliveredthereto simultaneously from the supply source. In this way pressurewithin the feed cylinder is weakened as compared with the pressureduring the forward stroke of the hammer, since during thelast namedhammer movement there is no escape of motive fluid from the feedEcylinder; consei quently, there is full line pressure in the feedcylinder for holding la'drill against the rock. By reducing the pressureWithin the feed cylinder, the force of the pressure of' the drill bitagainst the rook; reduced. durn los ing the return `stroke of the`ammer, thus `making the rotary movement of lthe drill 5 easier forthe'operator and at the same time diminishing the Wear upon the drillbit.

In myv improved construction, provision is further made foi-"regulatingthe supplyoI l motive fluid tothe motor or drill cylinder suppiy to thefeed cylinder, thus regulating the pressure in the feed cylinder tolxarmov with that in the drill cylinder. This is accomplished byactuating the throttle valve which is interposed between the motor andthegieed cylinder in the usual manner., @ther features of noveltyincluded in mi present invention will be understood by re erence to theaccompanying drawing taken in connection with the specification. y

1n the drawing, ni'fure 1 is a top plan view, partly in horizontalsection, illustrating. afhammer drili equipped with my improvements..Fig. 2 is a section taken on the line 2-2 of Fig. Fig. 3 is an elevationof the cylinder valve forming a part of the valve mechanism o1 theengine or'motor. Fig. 1 is a fragmentary' longitudinal section 'takenthrough the drill cylinder on the line Fig. il, Aand cutting thethrottle valve on the line L11--7 Fig. 12. Fig. 5 is a similar 'sectiontaken `through the engine construction on the line 5-5, Fig. 9, andcutting the throttle vaive on the line 5--6, Fig. 1,2.v Fig,

6 is a. similar section'talren on the line 6 6, Fig. 9, andthe line 5-6,Fig. 12. Fig. 7,

is a. similar section taken through the e'ngine structure on 'the line7--7, Fig. 9, and

the throttle valve on the line 4 7,

Fig. 12; Figi 8 is a, section taken through the engine on the line 8-8,Fig. 9, and through the throttle valvel on the line 8--8, Fig. 12. Figs.9, 10 and 11 are cross-sections e taken on the lines 9&9, 1.6-1.0 and`11-11,

respectively, Fig. v7. Fig. 12 is a vertical section Ataken through thethrottle valve mechanism on the line 12-12,4Fig. 13. Fig. 13 is a viewof the throttle valve mechanism iooln'ng in the direction of arrow 13,Fig. 12. Fig. .TL-ii is a section taken through the block or casing ofthe throttle valve showing the latter in elevation. Fig. 15,'is across-section taken through the throttle valve mechanism on the line155-15, Fig. 14. Fig. 16 is a cross-section taken through the throttleValve mechanism on the line fw-7, Fig. 12,;the, valve piece being.;shown yin a different pos1` tion'from that illustrated in Figs. 4 and 7.The same reference characters indicate the same parts in all the views.

From the brief' description oi the figures as already given, it willbeunderstood that I the relative positions of the throttle valve mechanismand the engine structure in Figs. Lt to 8, inclusive, must, at least sofar as some of the views are concerned, be considered diagrammatic, andthe excuse for this style of illustration in this particular instance isthat I am, by adopting this course, better enabled to illustrate theoperation and construction of the drill mechanism. It will, forinstance, be readily observed that if, in Fig. 4, the engine mechanismand throttle valve mechanism are relatively so arranged l`foi-mance ofits function is concerned.

that if the section is taken on the line 4 4, Fig. 9, through the engineand cuts the throttle valve horizontally, as shown in Fig. 4, if a viewas Fig. 7 be taken on the line `7-7, Fig. 9, or at right angles to line4 4, 70 the section would not show the throttle valve in horizontalsection as illustrated iny Fig. 7 of the drawing. It is, however,believed that the license which I have assumed in the preparation ofthis drawing may be excused, 1n 75 view of the great diflculty inclearly illustrat-ing -a structure of this character, where the portsand passages` are so complicated and where their relation to each otherin the throttle valve and engine mechanisms is so .o diflicultofcomprehension. In other Words,

it is thought that the clearness of illustration which is accomplishedby these views will compensate for any inconsistency which a criticalexamination ofthe'drawing would 86 disclose. The license which I haveindulged in is further believed excusable, in view of the fact that thecorrect illustration of the valve mechanism and its various parts is'accurately shown in Figs. 12 and 16; inclusive. 00

.The same reference characters indicate the same parts in all the views.

Let the numeral 5 designate the drill cylinder; 6 the valve mechanism oftheje'ngine; 7 the throttle valve mechanism; and 8 the 05 mechanism ofthe feed cylinder. l i

The feed cylinder is connected with the engine structure and throttlevalve mechanism -by means of rods 9, in the usual manner. Into the rearextremity of the engine adjacent 'the throttlev valve mechanism isinserted a member 1 0 having a centrally located core 12, throughwhichis formed a central cavity 1B, theyforward portion of which isclosed by a plug 14, threaded in the core, as shown at 15. Surroundingthis' core is the cylinder valve 16, which for the most part is of theusual construction. The wall of the valve, however, is provided with, anumber of separated shallow recesses or 110 cavities 17, which coperatewith circumferential grooves 18, 19 and 20, formed in the chester casing21 of the engine mechanism. By employing these shallow cavities'whichare separated bv cvlindrical segments of the structure, the valve isrelieved of considerable wear durin the operation of theA machine whilethe novel' structuredisclosed is equally effective so faras the propererhis` cylinder vulve is slidably mounted on the.' core 12, and has arange of longitudinal' movement, sufficient for opening and clos- -ingpurposes, the forward extremity of the valve when in the closed positionbeing in engagement 4with ashoulder 22, formed in the valve chest andsurrounding a forward "G51-With ports 4'6andv 47 formed in the valveopen or in its rearward position, as illustrated in Figs. 4 and 5, bythe action of the live air on a narrow shoulder 25, in the usual manner.In other words the circular' cavity 26' in the forward portion of thevvalve chest of the engine is always in communication with live4 air oryother motive Huid from the source of supply, the said fluid enteringthe throttlevalve 27, through a vertically disposed longitudinal.opening 2S, leading upwardly from the base 29 of' the valve block 30.From the opening 28, the motive `fluid passes forwardly through a port31, formed in the throttle valve, thence. through a port ,32, formed inthe Valveblock, thence into a forward cavity 33,

Vand thence in opposite directions through ports-34m passages 35, whoseforward ex;- tremities `communicate with the cavityQG. Hence,whether thecylindrical valve is in the open position, as shown in Figs. 4 and 5,

. or in the closed position as shown in Figs.

wardly in the drill cylinder until it engages f theI lstriking pin 37(see- F ig. l). In the hammer chamber a short distance forward of itsrear extremity are formed two ports 88, which communicate with passages39 extending rearwardly through the drill cylinder and the valve rchestand communicating -at their rear extremities with` a transverse passage40 formed rlh the base .of thecore member 10,.the passage 40communicating v'with the central, cavity 13 formed in.` the core, asheretofore explained. Leading from this central cavity are ports 4lformed in the'shell of the core and communicating :ith the space 42, inwhich the rear enlarged portion 43 l of the cylinder valve travels.These ports 41 are closed when the ,there will vbe no exhaustthroughthis path while the valve 16 remains in the open pos1t1 on. Asthe hammer continues its for- '.ward -movement the motive iuid forward.of.tli e,ha1mner will first exhaust through ports", -2 and. `passages3, extending rearwardly through the vshell of the cylinder A.ndcommunicating with lpassages 44 and 45, the passage 44 beinginy'communication chest and core member l0, respectively, the line ofcommunication being continued through a passage 48 of the valve block orcasing 30, whose rear extremity communicates with the atmosphere. Theexhaust the passage 45 passes inwardly through a port 49 to the space 4Qforwardof the rear extremity or face 43 of the cylinder valve, theexhaust from said cavity being through a lport 59., passages 53 and 54 f'formed in the valve chest, and core member l0, respectively, and thencethrough a passage 55 formed in the valve block 30, thence into a port 56formed in the valve piece of the throttle valve mechanism, and thencethrough a passage 57 formed in the valve block to the atmosphere. Theport 5G varies in size whereby the exhaust from the cylinder may beregulated and controlled by the proper adjustment of a valve piece ofthe throttle valve mechanism to cause the exhaustto harmonize with theintroduction of motive fluid to the hammer cylinder. After the hammerpasses the ports 2 and closes` the latter, the exhaust from the cylinderforward of the. hammer is continued through aport 58, and. passage 59formed the wall of the cylinden'and passage 60 ins-the valve chest,portG1 which communi- Cates with aA circumferential groove 19 formed in thevalve-chest adjacent the cylin der valve and in communication with thecavities 1i' of the last-named valve. From this" groove exhaustcontinues rearwardly thro-ugh ,recesses 17 of the valve 16 lto the lspace 42 forward of the shoulder 5l of the valve 1G. F rom this spaceexhaust contijnues tothe atmosphere through a4 port 7 5 and passagesy76, 77 and 78 on one side of the machine; while on the opposite side theexhaust"continues from the said space 42 u forward of the/'shoulder 51of the cylinder valve, through the ports 52, 53 and 54, the" passage 55,the graduated port 56, and the passage 57 .to the/atmosphere.

Just before the hammer engages the striking pin aport 65 is uncovered inthe cylinl der and the lived, motive iuid acting on the passages QG and(57 to a port (38 communi-- cating with the extreme rear portion of thecavity'42 in the .rear of the enlarged area 43 of the cylinder valve andthis live motive Huid acting on this enlarged area will serve to drivethe valve forwardly since the pressure on this enlarged area in theforward direction is suiiicient to overcome the other tendency, namely,the action of the live air on the small end of valve. The valve thenmoves to the closed position illustrated in Figs. 6, 7, and 8. The livemotive fluid is then cut off from the rear extremity of the hammerchamber and motive fluid from the feed cylinder 8 is introduced to thehammer chamber forward of the hammer by isa way of the following route,namely, from i the feed bar casing through an angular port cylindricalgroove 19; thence through ras` sages 61, 60, 59 and portv58, heretoforedescribed, into the hammer ylinder forward of the hammer. The latterthen begins its rearward travel and the exhaust from the hammer chamberin the rear of the hammer begins through the ports 38, the passages 39-and 40, tothe cavity 13; thence through the'ports 41 to the space 43`inthe rear of the cylinder valve, where the exhaust serves to hold thevalve in the closed position, the

esxape of the exhaust, however, in a restricted manner being continuedthrough a port 75, passages 76 and 77 formed in the valve chest, andcore member and thence through the passage 7 8 to the atmosphere. Theexhaust also passes from the space 43 in therear of the cylinder valve,through the ports 52, 53 and 54, the passage 55, the port 56 of thethrottle valve piece and the passage 57 to the atmosphere.

VThe exhaust as just explained continues until the hammer closes theport 38, after which the air cushionsl l'ietween the hammer and the rearextremity of its chamber and acts on the forward extremity of thecylinder valve and in` conjunction with the action of'the live motivefluid or the small shoulder 25 serves to move t e cylinder valverearwardly tothe open position. As soon as the. ports 3S are covered,the ports. 2 are opened forward of the hammer and the exhaust from. thehammer chamber in front ol the hitter commences through the passages 3,and continues on` one side of the machine through the ports 4G and 47and the passage 48 to the atmosphere; while on the opposite side theexhaust from the hamm'er chamber in front of the hammer enters the space42 and acts'upon the shoulder 51, which also aids in impartingr theopening movement to the cylinder valve. The exheretofore explained.

4that a the hammer inactive, thevfeed bar cylinder 8 isiin communicationwith the atmosphere through a cavity 79 in the throttle valve I block orcasing, a port 80, 'a small recess 81 vin the throttle valve, a passage82 in the.

throttle valve and a passage 83 in the lthrottle valve block or casing.This condi- 1 tion allows the air in the feed bar casing to exhaust tothe atmosphere as there is no necessity for holding the drill againstthev rock when not in use. vWhen this condition exists thethrottle-.valve piece 27l is turned considerably farther in the directimfof thearrow, in Fig. 15, than is illustrated, or so f port or passage 84 inthe throttle valve will extend beyond the port in the direction of thevalvesrotary movement, indicated by the arrow in said figure.

Now, when it is desired to set the drill against the rock'the throttlevalve piece will be rotated in the direction opposite the said arrow,first to turn the port 84 into com.

munication with the port 80, .in which event the motive fluid whichenters through the passage 28 of the throttle valve piece will pass tothe feed bar casing and supply the necessary pressure therein to holdthe drill against the rock. At this time, however;

the hammer is in a conditionof rest as the live motive fluid has notbeen introduced toe.,

the hammer chamber. start the hammer, the throttle valve piece is turnedfarther in the direction opposite that of the arrow, or until theport 31in th' throttle valve piece ,is brought into communication with the port32 ofthe throttlel live motive fluid passesvfr the source of Asupply tothe hamner chamber in the rear of the latter to dri\'e the hammerforwardly'. as heretofore explained. f

lVhen the throttle valve 'piece is adjusted to deliver the maximum plyofmotive fluid to the engine and thie,v Aeed bar casing, the exhaustport 56 in lili; throttle valve piece occupies approximafely theposition illustrated in Figs. 5 and 1,6. rotary` action of this valvie`piece,until the exhaust port occupies slh position, the

opening movement of the. 7port 31 in the- During the' the opening ofThen, in order to valve block or casing, in hich` event the-,-

it is desiredl to increase theexhaust through.

the variable port'G, the rotary' action of the throttlevalve continuedin the direction A opposite, 'the arrow,L in Fig. 15, and thisvportion/of this port is brought vwith rthe last-named passage.' .Duringthis movement of the throttle. valve, the rearmovement will increase theexhaustthrough theport 5,6 inasmuch as this action of the valve? pieceincreases thedepthfof the portion of the port 'l'lwhich is brought intoregister with the passage- 7 until the deepest into register valve willopen before the hammer reaches it should remain open or during theforward the rear extremity of itschamberfand when the exhaust throughthe portv 56 is` at itsA maximum the 'strokes of the hammer will vbevery shoitv and exceedingly rapid. Atrthe same time the portsl and 90are so constructed that the adjustment of thethrottl'e valve for thepurpose of increasing the ex haust through the port 56 does not vary the'volume of motive liuid which passes to the engine sind the feedbarcylinder. rFhis is a very important feature of my. improve ment andenables me to accomplish an'object,

not heretofore attainable in 'previous constructions, so far as lamaware.

in further explanation of the construcf;y tion, it may be stated that a.relatively small w port 91 is in communication with the space or cavity42. rhis port communicates with av small passage 92 leading to theatmospliers and permits the escape of any motive y fluid that may leakinto the cavity 43 in the rear of the cylindervalve when the lat` ter isinthe open position and' obviates anytendency to close the cylindervalve whentravel of the hammer in the'cyli'nder.

In further explanation of the construction, it may be stated that asmall port 4 (see Fig. 4) is for the purpose of compensating for uanyslightlv irregularity,-should it occur-,

70. lt is of importance only as, on account of its relatively smallcross-v sectional area, it does not interfere with the action of themechanism of the 'machine as described, when the hammer 1s moving atmedium or maxlmum speed.

Still another yfeature consists in' forming an interior annular groove101 at the forf ward' extremity of lthe cylinder valve 1 6,

which communicates at its forward extremity when the cylinder valve isopen, with the cavity 26, and at its opposite extremity with a port 100communicating With Consequently, the last-named as regards thesimultaneous opening ya passage 102 which leads to they central cavity13. The said groove 101, the port 100 and the passage 102 are relativelysmall, their only object being to allow enough mot-ive fluid'to passduring the first part of the-forward movement of the hammer 36, i to illthe passages 39 and 40 by the'time the ports 38 are uncovered, thusobviating any dinnnution of the motive fluid pressure acting on thehammer, which diminution of preure would result by the filling ofthesaid passages with the motive fluid from behind the hammer as soon asthe ports 38 Wereuncovered, if the said passages had not already beenlled.

`Iclaimv 1. In mechanism of the character described,'they combinationwith a motor inclutling a cylinder and a hammer mounted gto-'reciprocatetherein, of a valve for varying .the 'supplyv of motive fluid to 4themotor, saidv valve bein also equipped to gradually and continuous yincrease the exhaust from the motor as' the valve Ais moved from closedto.v fully open position.4

2. In mechanismof the class described,

the combination of 'a motor and feed bar casing, of' a Vvalve interposedbetween the motor and said fcasing and adjustable to control'the passageof motive fluid to both, the saidy valve being also' equipped togradually and continubusly increase the exhaust from the motor as thevalve is moved from the closed to the 'fully open position.

3. The combination with a motor, including a cylinder and a hammermounted to re-` ciprocate4 t ereinl and a feed bar casing, of

a valve int rpcsed between the motorl and said .casing an passage ofmotive liuid to both the motor and casing,l thelsaid valve being alsoequipped to gradually and continuously increase the exhaust from themotor as the valve is sition.

4. vThe combination with a motor and feed barY casing, of a valveinterposed between the motor and said casing to control the passage ofmotive fluid to both, and equipped with a port arranged to yary theexhaust from the motor while the supply to bothmotor and feed bar casingremains uniform. i l

5. Thef combination. with a motor and feed'barnasing, of a valveinterposed between th said motor and casing to control the passageofmotive fluid to both, and equipped with a port arranged. to increase theexhaust increased to both casingand motor until the moved from theclosed to the fully open poadjustable to controlthe *i from the motor asthe supply is n is reached and without varying the supply to either themotor or casing.

7. The combination with a cylinder and a piston mounted to reciprocatetherein, a movable valve for controllingthe supply of motive fluid toand its exhaust from the cylinder, the valve ha vine; ditferentialpressure areas and the pressure ol the exhaust 0n the larger areaserving to hold the valve closed during the rearward movement of thehammer, and a second valve having a port ai ranged in the path of suchexhaust and adjustable to vary the length of time during which thepressure of the exhaust on the larger area of the first-named valve isexerted for the purpose set forth.

S. rIlle combination with a cylinder, a hammer mounted to reciprocatetherein and a movable valve for controlling the supply of motive fluidto and its exhaust from the cylinder, the valve having differentialpressure areas and the pressure 'ot' the exhaust y on the larger areaserving to hold the valve closed during the rearward movement of thehammer, against the tendency of the live motive fluid on the lesser areato open the said valve, and a second valve lhaving ports through whichthe supply and exhaust to and from.' the cylinder pass, the second valvebeing;v adjustable to 'increase both the supply and exhaust until themaximum supply is reached, and to furtherincrease the exhaust withouttfhaluginpthe supply, until a predetermined maximum cxhaust is attained.

l). The combination with a cylinder, a hammer mounted to reciprocatetherein and a movable valve `for controlling the supply of motive fluidto and its exhaust from the cylinder, the valve having` ditlerentialpressure areas and the pressure of the exhaust on lthe larger areaserving to hold the valve closed during the rearward movement of thehammer, and a second valve having ports through which the supply andexhaust to and from the cylinder pass, the second valve being adjustableto increase both the supply and exhaust until the maximum supply isreached and to further vary the exhaust within a pre-determined rangeafter the' maximum supply limit is attained, without varying the supplyfor thev purpose set forth.

10. In a tool of the class described, the

combination with a motor including a cylinder and a motive Huid actuatedhammer iounted to reciprocate therein, a feed cylinder for holding themotor to its work, the motor having a movable valve Ator regulating; thesupply' and exhaust to and from. the cylinder, the said valve having,rdil'lerential pressure areas upon the larger of which the exhaust actsto hold the valve lclosed during' the return of thehammer, and a secondval ve interposed between the motor and cylinder and having;` portsthrough which the supply to the `motor and t'eed cylinder passes and aport through which the exhaust from the motor cylinder passes, chesecond valve being adjustable to control the supply to both cylindersand the exhaust from the motor cylinder and to vary the lasts namedexhaust. Within a Ipre-determined range Without varying the supply tothe nio-I tor or feed cylinder.

11.x .Tn a rock drill, the combination of a motor and feed cylinder,'the motor including a cylinder and a hammer mounted to reciprocatetherein, the motor having a valve movably mounted to regulate the supplyand exhaust of the motive luid to and from the hammer cylinder, and asecond valve in.M terposed between the motor and feed cylinder andhaving; ports arranged. for the passage of the motive fluid supplydirectly from its source lto both cylinders, said drill hav-- mg apassage for the transmission ol me tive fluid from the feed cylinder tothe motor cylinder for the return of the han/nner, said passage beinglarger than the said port leading to the feed cylinder and said passagebeing arranged toibe controlled by the motor valve.

12. In apparatus of the class describek the combination with a motorincludi cylinder, a hammer mounted to reciprmate therein and a valvemovably mounted to regulate the supply and exhaust of motive fluid toand from the cylinder, and meaf f r subjecting the valve to a portion ofthe haust from the cylinder forward of. the hammer shortly before thehammer has reached its limit of rearward travel to aid in openii thesaid valve.

13. In an apparatus of the class described, the combination of a motor,a feed cylinder, a movable piston therein and mechanism. whereby a lowerpressure prevails in feed cylinder when the hammer is moving` rearwardlythan when the hammer is moving forwardly or toward the striking `pin. z

14. In a Huid driven rock drill, a slide. valve having surfaces ofdifferent areas at its ends, means for subjecting the surface of greaterarea to the pressure of the exhf ing `fluid while the valve is in onepo` and means for regulating the f exhaust.

mii

Valve having surfaces of different areas at its ends, said smallersurface being constantly under the influence of line pressure, means forsubjecting the said larger surface to the pressure ot the exhaustingHuid, while the valve is in one position, and means for regulating thespeed of the exhaust.

16. In apparatus of the class described, the combination with a motorincluding a cylinder, a hammer mounted to reciprocate therein, and a`valve movably mounted to regulate the supply of motive fluid to thecylinder, said cylinder havingan exhaust passage arranged to beuncovered by the hammer when near its rear limit of movement only, saidvalve having a projection and said cylinder having a port adapted tomaintain communication between the said passage and one side ot' saidprojection.

17. In a rock drill, a feed cylinder, a. hammer cylinder, a motor valveinterposed between said cylinders, said drill having passages forfeeding motive f luid continuously to said valve, a feed cylinder and apassage leading from the feed cylinder to the forward end of the hammercylinder, said last named passagebeing arranged toV be controlled by themovement of the motor-valve.

18. In a rock drill, a feed cylinder, a harnmer cylinder, a motor valveinterposed between said cylinders, said drill having passages forfeeding motive fluid continuously .to said valve, a feed cylinder and apassage leading from the feed cylinder to thefor ward end of the hammercylinder, said last named passage being larger than the feed passage tothe feed cylinder and being ar' ranged to be controlled by the movementof the motor valve.

19. In a rock drill, a hammer, a hammer cylinder, a motor valve forcontrolling the flow of motive fluid to'said cylinder, the

latter having an exhaust passage extending through and controlled bysaid valve, and means for regulating the s1ze ot said pas- Sage at onepolnt.

